1. Field of the Invention
This invention relates to a resin composition with improved mechanical characteristics, and more particularly, to a resin composition with improved mechanical characteristics that comprises an aromatic polyester copolymer, polyamide and a specified metal compound.
2. Description of the Prior Art
An aromatic polyester copolymer prepared from terephthalic acid and isophthalic acid or functional derivatives thereof and a bisphenol or functional derivatives thereof is a heat resistant, thermoplastic resin having high heat distortion temperature and high heat decomposition temperature as well as good mechanical and electrical properties. It is widely used in fields where engineering plastics of high quality are required. However, because of high heat distortion temperature, it is less moldable than other thermoplastic resins; for instance, making an injection molded article of it requires high molding temperature and injection pressure whereas the resulting molded article often develops a sink mark, flow mark or excessive internal strains.
Molded articles with sink marks, flow marks or excessive internal strains are not only poor in appearance but are greatly affected in mechanical properties so it frequently occurs that the excellent performance of the resin from which they are molded will not be exhibited to the fullest. Depending on the kind of molded articles, the flow length is sometimes insufficient to provide a perfect product. Therefore, it has been required that good engineering plastics be excellent not only in various properties but in moldability also. However, it is also known well that a polymer blend intended to improve the moldability of a heat resistant engineering plastic tends to decrease its heat distortion temperature. Furthermore, while an aromatic polyester copolymer has the advantages mentioned above, it can only be used in limited applications because of insufficiency in resistance to organic solvents.
Polyamides are very excellent in resistance to organic solvents, wear resistance and moldability, but they are not adequately heat resistant as typified by polycaprolactam and polyhexamethylene adipamide which have a heat distortion temperature of 56.degree. C. and 59.degree. C., respectively. As a further disadvantage of polyamides, they have high hygroscopicity and are known to be subject to dimensional variation, changes in mechanical performance and reduction in electrical properties.
A resin composition comprising an aromatic polyester copolymer and polyamide has considerably higher heat distortion temperature than a polyamide as well as has adequately higher moldability and solvent resistance than an aromatic polyester copolymer. The improvement so much exceeds what is presumed an additive effect from the proportion of the two polymers that constitute the resin composition. Therefore, the resulting composition has every useful property in that it retains not only the excellent tensile strength, bend recovery characteristics and dimensional stability of the aromatic polyester copolymer but the high crack resistance and wear resistance of the polyamide (see Japanese Patent Application (OPI) Nos. 4146/75 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") and 98765/77).
It turned out, however, that articles made by, for example, injection molding of a resin composition comprising an aromatic polyester copolymer and polyamide had the following defects: the molded article easily breaks at a thin-walled portion such as gate or at a long narrow rod-like projection especially when it is absolutely dry, thus, imposing limitations on practical application such as when the article is released from the mold as well as when the product design is to be decided. What is more, even a relatively thick-walled article easily cracks upon impact such as a drop impact and a falling-ball impact especially when it is absolutely dry. All these phenomena constitute a considerable limitation on the usefulness of such resin compositions.
Examples of prior art resin compositions that comprise an aromatic polyester and metal compound include Japanese Patent Application (OPI) No. 51048/73 which uses an Sn compound for improving the heat resistance and light resistance of the resulting resin composition, Japanese Patent Application (OPI) No. 51152/75 which uses a variety of metal soaps for improving the moldability of the composition, Japanese Patent Application (OPI) No. 152953/77, Japanese Patent Application (OPI) No. 152954/77 (corresponding to U.S. Ser. No. 860,411) and Japanese Patent Application (OPI) No. 16558/77 (corresponding to U.S. Pat. No. 4,097,431) all of which use metal salts of carboxylic acid to prevent occurrence of water crazing.
It is known to incorporate a variety of Cu compounds into a polyamide as an agent for providing heat resistance. However, no example has been known of incorporating a metal compound into a resin composition of aromatic polyester copolymer and polyamide nor has the effect of such incorporation been known.